Moisture barrier composite film of silicon nitride and fluorocarbon polymer and its use with an on-cell tester for an electrochemical cell

ABSTRACT

A light transparent moisture barrier useful for preventing moisture from destroying the effectiveness of a moisture sensitive cell condition tester on an electrochemical cell, comprises a plurality of very thin layers of amorphous silicon nitride and a hydrophobic fluorocarbon polymer on a flexible, polymeric substrate. The layers are formed on the substrate by a deposition process such as sputtering. The thickness of any individual layer is less than one micron.

This application is a division of application Ser. No. 08/376,700 filedJan. 23, 1995 now U.S. Pat. No. 5,593,794.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to a light transparent, moisture barrier filmcomposite. More particularly, this invention relates to a lighttransparent, thin film composite comprising layers of silicon nitrideand fluorocarbon polymer which is useful as a moisture barrier for amoisture sensitive on-cell tester, a process for making said barrier andto an electrochemical cell having a moisture sensitive on-cell testerand said barrier.

2. Background of the Disclosure

The use of cell condition testers, such as thermochromic voltagetesters, to visually indicate the condition of an electrochemical cell,commonly referred to as a battery, has become very popular and providesa value added advantage to the battery manufacturer and to the consumer.These testers are used with primary electrochemical cells, although theycan also be used by consumers to test the condition of a secondary orrechargeable electrochemical cell if desired. The most popular testerpresently in use is a thermochromic material in contact with anelectrical resistance element which forms an integral part of a batterypackage in which the batteries are alkaline primary cells. The userplaces the terminals of the cell between the contacts of the tester andsqueezes the contact ends of the tester to make electrical contact withthe cell terminals which are the ends of the cell. The resistanceelement of the tester is heated in proportion to the cell voltage andthe thermochromic material provides a qualitative indication of thecondition of the cell over a range indicating "good" or "replace". Thiskind of tester is disclosed, for example, in U.S. Pat. No. 4,723,656. Anintegral, thermochromic package tester which can also be removed fromthe package is disclosed in U.S. Pat. No. 5,188,231. More recently,on-cell testers have been developed in which the cell conditionindicator is an integral part of the cell label. These on-cell testersinclude both the thermochromic type and a new, electrochemical type oftester. An example of a thermochromic type of on-cell tester isdisclosed in European Patent Publication No. 0 523 901 A1, thedisclosure of which is incorporated herein by reference. Unlike thethermochromic type which employs a resistance element to produce heatand which can therefore not be permanently attached to the terminals ofthe cell without continuously discharging it, the new electrochemicaltype does not draw current from the cell and can therefore bepermanently attached to the terminals of the cell without dischargingthe cell. This new type of tester is disclosed in U.S. Pat. Nos.5,250,905 and 5,339,024 the disclosures of which are incorporated hereinby reference. As is disclosed in U.S. Pat. No. 5,355,089 someelectrochemical types of on-cell condition testers employ hygroscopic orotherwise moisture sensitive electrolyte compositions and means arenecessary to prevent moisture from reaching the electrolyte which willimpair the effectiveness of the tester. This patent discloses a numberof solutions to this problem, the best of which is mica. However,although relatively inexpensive, mica is not available in long ribbonsor other forms which permit it to be rolled into a roll of mica which isneeded for economically viable commercial production methods.

SUMMARY OF THE INVENTION

The invention relates to a light transparent composite useful as amoisture barrier, which comprises at least one layer of silicon nitrideand at least one layer of fluorocarbon polymer, preferably at least twolayers of silicon nitride and at least two layers of fluorocarbonpolymer and which is formed by depositing or forming said siliconnitride and said fluorocarbon polymer layers onto a substrate. In oneembodiment, the composite of the invention comprises at least fourlayers, with at least one layer of silicon nitride and at least onelayer of fluorocarbon polymer on one side of the substrate and at leastone layer of silicon nitride and at least one layer of fluorocarbonpolymer on the opposite side of the substrate. In another embodiment,more than one layer of the silicon nitride and more than one layer ofthe fluorocarbon polymer are on one side or surface, only, of thesubstrate. In this embodiment, and in the embodiment in which there ismore than one layer of each of the silicon nitride and the fluorocarbonpolymer on each of opposite sides (e.g., top and bottom) of thesubstrate, the composite comprises alternating layers of silicon nitrideand fluorocarbon polymer. The invention includes multilayer compositesin which there is more than two layers of each of the silicon nitrideand fluorocarbon polymer, with the actual number of layers depending onthe desired properties of the composite and being limited only by theability of the practitioner to deposit a large number of layers. In oneembodiment in which the composite of the invention is used as a moisturebarrier for an on-cell tester for an electrochemical cell, the substrateis a flexible polymer and the composite is a flexible, lighttransparent, thin film composite in which the thickness of each of thesilicon nitride and fluorocarbon polymer layers is less than one micron.In a further embodiment, the composite of the invention is used as atransparent packaging material for moisture sensitive materials andarticles. When used as a moisture barrier for an on-cell tester, thelight transparency of the composite enables a user to see the conditionof the cell as exhibited by color, indicia or other visual means used bythe tester to indicate the cell condition. By on-cell tester is meant atester which visually indicates the cell condition and is permanentlyattached to the cell either by means of the cell label or by othermeans, although the invention is not limited to this embodiment. Onetype of a moisture sensitive, on-cell tester for which the moisturebarrier composite of the invention is useful, is a tester which includesat least one hygroscopic material which, if it absorbs water vapor,impairs or destroys the effectiveness of the tester. Another type is atester which includes at least one component requiring the presence of apredetermined amount of water to function and which therefore needs amoisture barrier to maintain that level of water in the tester.

Both the silicon nitride and the fluorocarbon polymer are waterinsoluble, with the fluorocarbon polymer selected to have as low a watervapor permeation rate as possible for moisture barrier applications. Formoisture barrier applications it is preferred that the fluorocarbonpolymer is hydrophobic. The process for making the multilayer compositecomprises depositing a layer of silicon nitride onto a substrate,followed by depositing a layer of fluorocarbon polymer over the siliconnitride layer. If more than one layer of the silicon nitride andfluorocarbon polymer are required, the alternating layer depositionprocess is continued until the desired number of layers have beenapplied. Thus, the composite of the invention is distinguished fromlaminates in which various pre-existing layers are adhesively orotherwise bound to each other, in that the alternating layers of thecomposite of the invention are formed in-situ on the substrate and onother layers of the composite, by deposition or coating processes whichinclude sputtering, physical vapor deposition, including plasma-enhancedphysical vapor deposition, chemical vapor deposition and the like.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 schematically illustrates a four layer moisture barrier on apolymeric substrate according to the invention.

FIG. 2(a) schematically illustrates a cross-section of an on-cell testeron a cell with a moisture barrier of the invention and

FIG. 2(b) schematically illustrates, in partial phantom, a side view ofa cell having an on-cell tester and a moisture barrier of the invention.

DETAILED DESCRIPTION

FIG. 1 schematically illustrates a thin film moisture barrier 10 of theinvention as comprising a flexible plastic substrate 12, with a layer ofsilicon nitride, layers 14 and 16, deposited on both sides of thesubstrate. A layer of a hydrophobic, fluorocarbon polymer, layers 18 and20, is shown as deposited over each of the silicon nitride layers. Thus,the multilayer moisture barrier illustrated in this Figure is a fourlayer composite (exclusive of the substrate). If desired, the four layercomposite is deposited on only one side of the substrate. Additionallayers of the silicon. nitride and the fluorocarbon polymer arealternately deposited over each other on either one side of thesubstrate or on both sides of the substrate to form a six, eight, ten,twelve or even a one hundred layer composite, if desired. Thus, a firstlayer of silicon nitride is deposited on one or both sides of thesubstrate and then a first layer of fluorocarbon polymer is depositedover the silicon nitride layer or layers. A second layer of siliconnitride is then deposited over the first layer or layers of fluorocarbonpolymer and a second layer of fluorocarbon polymer is then depositedover the second layer or layers of silicon nitride. This alternatinglayer deposition process is repeated until a thin film, multilayercomposite having the desired number of layers is formed. The thicknessof each of the silicon nitride layers is within the range of from about200 angstroms to about 5,000 angstroms, preferably from about 250angstroms to 2500 angstroms, and still more preferably from 500 to 1,000angstroms. The thicknesss of each of the fluorocarbon polymer layers iswithin the range of from about 250 angstroms to one micron andpreferably from 300 to 5,000 angstroms. Increasing the thickness of thesilicone nitride will increase its tendency to crack and increasing thethickness of the fluorocarbon polymer layer increases stress in eachdeposited layer, which increases the tendency of the polymer layers topeel away from the silicon nitride. On the other hand, decreasing thelayer thickness increases the possibility of void formation andincomplete coverage. Either of these situations reduces theeffectiveness of the composite as a moisture barrier. The number oflayers and layer thickness will, of course, depend on the intended useof the multilayer composite and on the particular fluorocarbon polymer.Further, the silicon nitride is relatively brittle and is prone to crackwhen flexed or bent. Depositing a layer or coating of polymer over thesilicon nitride layer greatly reduces its tendency to crack and alsoprotects it from damage when handled. In the embodiment illustrated inFIG. 1, both sides or surfaces of the silicon nitride layers areprotected by an adjacent polymer layer, one of which is the fluorocarbonpolymer and the other is the substrate. It is a preferred embodiment inthe practice of the invention that the surface of the silicon nitride isprotected and that the outer layer or layers of the composite arepolymeric. If desired however, the outer layer or layers of thecomposite may be silicon nitride.

The invention includes embodiments in which (a) not all of the siliconnitride layers of the composite are of the same thickness, (b) not allof the fluorocarbon polymer layers are of the same thickness and (c)combinations thereof in which not all of the silicon nitride layers areof the same thickness and not all of the fluorocarbon layers are of thesame thickness. Other embodiments include a composite in which not allof the fluorocarbon polymer layers are of the same composition and alsoin which some of the polymer layers are not fluorocarbon polymers. Inyet another embodiment, substrate 12 is a web having a releasablesurface on which the first layer is deposited, so that the multilayercomposite is removed and used without the substrate on which it wasformed. In still another embodiment, a composite of the invention isformed on a first substrate which is a web having a releasable surfaceand then transferred to a second substrate to which it is attached byany suitable means. For most applications a substrate is needed forstrength to enable the multilayer composite to be handled and used inmanufacturing processes without breaking. As set forth above, thetransparent composite of the invention is useful as a thin film moisturebarrier for electrochemical testers and as packaging material formoisture sensitive foods, chemicals, biological materials andpharmaceuticals, electronics and articles. In addition to its moisturebarrier properties and transparency to visible light, another advantageof the composite of the invention is the chemical inertness of thesilicon nitride and fluorocarbon polymer. Those skilled in the art willappreciate that the composite of the invention may also be designed andused for other applications, including optical applications such asselectively transmitting and reflecting various portions of theelectromagnetic spectrum. The composite of the invention is differentfrom composites of the prior art both as to the combination of thesilicon nitride and the fluorocarbon polymer, and also in that thesilicon nitride layers and the fluorocarbon polymer layers are formed bydeposition processes and not laminated by adhesively or otherwisebonding preformed ribbons or sheets of material to form a layeredstructure. However, it is also within the scope of the invention, andforms one embodiment thereof, that one or more composites of theinvention may be laminated to each other or to other composites ormaterials, or combinations thereof, to form a laminated structurecomprising at least one and preferably two or more composites of theinvention.

The silicon nitride layers formed by the deposition processes useful inthe practice of the invention are light transparent and amorphous. Thesilicon nitride also has very good resistance to moisture permeation andgood corrosion resistance to a variety of corrosive environments, inaddition to being light transparent. As set forth above, thefluorocarbon polymer useful in the practice of the invention is lighttransparent and preferably hydrophobic. One particular type offluorocarbon polymer useful in the practice of the invention comprises afamily of light transparent, amorphous polymers having excellentchemical resistance formed by reacting2,2-bistrifluoromethly-4,5-difluoro-1,3-dioxole (PDD) with itself toform a homopolymer or by reacting PDD with other fluorine containingmonomers, such as tetrafluoroethylene (TFE), vinylidine fluoride,chlorotrifluoroethylene, vinyl fluoride, and perfluoro(alkyl vinylethers). Commercially available copolymers of PDD with TFE, where PDD isthe principle monomer, are available as Teflon AF from DuPont.Illustrative, but nonlimiting examples of other fluorocarbon polymersuseful in the practice of the invention include polytetrafluoroethyleneor PTFE as it is known, copolymers of TFE with hexafluoropropylenecommercially available as Teflon FEP from DuPont, and copolymers of TFEwith perfluoro(alkyl vinyl ethers) commercially available from DuPont asTeflon PFA. While some or all of these fluorocarbon polymers may belight opaque in bulk form, thet are light transparent at the layerthickness used in the invention.

The layer deposition processes useful in the practice of the inventioninclude the various PVD processes such as sputtering and evaporation.Also useful is plasma polymerization, monomer vapor deposition, variouschemical vapor deposition, low pressure chemical vapor deposition andplasma enhanced chemical vapor deposition processes, which are known tothose skilled in the art. High speed methods for applying a coating orlayer to a substrate on a roll or reel are also known and are disclosed,for example, in U.S. Pat. Nos. 4,543,275 and 5,032,461. Generally, onlyone layer at a time is deposited in a vacuum chamber. Thus, a layer ofsilicon nitride is deposited on one or both sides of the substrate. Thenthe target material in the vacuum chamber is changed to the fluorocarbonpolymer or the silicon nitride coated substrate is transferred toanother chamber in which the target material is the fluorocarbonpolymer. The fluorocarbon polymer is then deposited as a layer over thesilicon nitride layer(s). If desired however, at least one layer ofsilicon nitride and at least one layer of fluorocarbon polymer aredeposited on one or both sides of the substrate within one vacuumchamber by employing in the chamber, at least two deposition sputtertargets. For example, in a vacuum chamber in which the layer depositionoccurs by magnetron enhanced sputtering, the substrate is one electrodeand the target material to be deposited on the substrate is the otherelectrode, with the plasma inbetween the electrodes in the case ofdepositing a layer on one side of the substrate. Alternately, the targetmaterial and plasma are over both sides of the substrate for depositinga layer on both sides at the same time, in which case a layer of eithersilicon nitride or fluorocarbon polymer is deposited over both sides ofthe substrate or silicon nitride coated substrate. Further if thesubstrate is a moving strip or film, then more than one material isdeposited in one pass of the substrate by sequentially employing morethan one target in the vacuum chamber. Thus, if the substrate is amoving strip or film, as the substrate moves past the first target orset of target which, for the sake of illustration is the siliconnitride, a layer of silicon nitride is deposited on one or both sides ofthe substrate. As the silicon nitride coated substrate continues to moveto a second target or set of targets in the chamber downstream of thefirst target(s), a layer of fluorocarbon polymer is deposited over thesilicon nitride layer, and so on. Thus, a multiple number of layers maybe applied to the substrate in one pass of the substrate in the vacuumchamber to form a composite such as that illustrated in FIG. 1, or acomposite having more less layers than that illustrated in FIG. 1. Thisprocess permits production of a relatively large volume of the compositeof the invention at a reasonably manufacturing cost.

As set forth above, U.S. Pat. Nos. 5,250,905 and 5,339,024 discloseon-cell testers which may contain one or moisture sensitive componentsand which therefore require that a moisture barrier be employed inconjunction with the tester to prevent moisture from impairing theeffectiveness of the tester as disclosed in U.S. Pat. No. 5,355,089. Onemethod which has met with some success is the use of a small sheet ofmica disposed over the on-cell tester and sealed by means of a suitablemoisture resistant material, such as polyisobutylene, as disclosed inthe '089 patent. FIGS. 2(a) and 2(b) schematically illustrate a sideview of an on-cell tester on a cell with a moisture barrier of theinvention and a top view in partial phantom, respectively. Thus, FIG. 2schematically illustrates an electrochemical cell 50 having an on-celltester 60 of the type disclosed in the '089 patent and which contains atleast one hygroscopic component (not shown), with a thin film,multilayer moisture barrier of the invention 70 disposed over the testerand sealed to the outside of the metal cell container 52 by means ofsealant 62 and with plastic label 70 wrapped around the cell anddisposed over the tester, seal and moisture barrier. Tester 60 is about10 mils thick and is attached to the positive 54 and negative 56terminals of the cell by means not shown. As disclosed in the '089patent, tester 60 contains, for example, a polymer electrolytecontaining 0.5M lithium trifluorosulfonate in an aprotic solvent (i.e.,ethylene carbonate and propylene carbonate) and polyvinylidine fluoride,which is very hygroscopic. The sealant material is, for example, amaleic anhydride modified polybutylene elastomer available a VestoplastV3645 from Huls, Inc. in Piscataway, N.J. The label is a PVC filmwrapped around the cell and moisture barrrier/tester/sealant and thenheat shrunk. As a practical matter, for use as a moisture barrier for anon-cell tester on an electrochemical cell, such as the on-cell labeltesters disclosed in the patents referred to above, the total thicknessof the moisture barrier is no greater than about one and one-half milsand preferably within about one mil or 25 microns.

The moisture barrier of the invention 10 comprises a one mil thickpolyethylene naphthenate film as the substrate over both sides of whichhas been deposited a layer of silicon nitride, with a layer of Teflon AFdeposited over each layer of silicon nitride, as is illustrated in FIG.1, to yield a moisture barrier essentially 1 mil thick and having amoisture vapor transmission rate of less than 8 micrograms of water persquare inch of surface area over a twenty four hour period measuredaccording to the procedure set forth below. Each silicon nitride layeris 500 angstroms thick and each layer of Teflon AF is 1,500 angstromsthick. The silicon nitride layers and the Teflon AF layers are depositedby radio frequency (RF) magnetron sputtering at 31° C. in argon, at apressure of 1.5 millitorr.

The water permeation or the moisture vapor transmission rate of themoisture barrier composite is measured by placing a strip of polymerelectrolyte 0.25 inches wide, 1 inch long and 3 mils thick, and whichcontains 70 wt. % of 0.5M lithium trifluorosulfonimide salt in3-methylsulfolane and 30 wt. % polyvinylidine fluoride, onto a sheet ofmica 1.5 mil thick. A 1 inch wide and 1.7 inch long rectangle of themoisture barrier of the invention is placed over the strip and thensealed to the mica by a maleic anhydride modified polybutylene elastomersealant 2.5 mils thick to form a laminate, as generally illustrated inFIG. 2. Thus, the hygroscopic strip is sealed between the mica andmoisture barrier by means of the sealent. This is done under anhydrousconditions in a sealed glove box. The so-formed laminate is then kept at60° C. and 100% relative humidity for one week, after which the strip ofpolyvinylidine fluoride containing the solvent and salt is removed andanalyzed for its water content by Karl Fischer titrometry. This is thetest method and test conditions referred to and used in the examplesbelow.

The invention will be further understood by reference to the examplesbelow, in all of which the moisture barrier is light transparent.

EXAMPLES Example 1

In this example a 1 mil thick film of polyethylene naphthenate (Kalodex)is the substrate and a 500 angstrom thick layer of silicon nitride is RFsputter coated on each side of the substrate in 1.5 millitorr of argonfrom a silicon nitride target. The silicon nitride layers deposited bythis process are amorphous. After this, a 1500 angstrom thick layer ofTeflon AF is RF magnetron sputter coated over each of the two siliconnitride layers in 1.5 millitorr of argon from a Teflon AF target. Theso-formed light transparent, thin film, multilayer moisture barrier hasa water vapor transmission rate of less than 8 micrograms of water perin² of surface per 24 hour period, as determined by the test methodreferred to under the DETAILED DESCRIPTION above.

Example 2

In this example a 1 mil thick film of polyethylene naphthenate (Kalodex)is the substrate and is sputter coated in 1.5 millitorr of argon withsilicon nitride to form a layer or coating of amorphous silicon nitrideabout 500 angstroms thick only on one side of the substrate. PTFE isthen sputtered onto the silicon nitride layer to form a PTFE layer 1500angstroms thick. This process is repeated once to form a lighttransparent, thin film, multilayer moisture barrier comprising fouralternating layers of amorphous silicon nitride and PTFE (2 siliconnitride and 2 PTFE) on one side of the substrate and the moisturebarrier has a water vapor transmission rate of 28 micrograms of waterper square inch of surface area over 24 hours using the test method ofExample 1.

Comparative Example A

This experiment is similar to that of Example 1 with respect to the RFsputtering in argon, the polyethylene naphthenate substrate and moisturetransmission test method. In this experiment, one side only of thesubstrate is sputter coated with a layer of silicon oxide 500 angstromsthick from an SiO₂ target and this layer of silicon oxide was thensputter coated with a layer of PTFE 500 angstroms thick from apolytetrafluoroethylene (PTFE) target. This process was repeated twice,alternately depositing a silicon oxide layer and a Teflon AF layer toproduce a light transparent composite comprising six alternating layersof SiO_(x) and PTFE (three SiO_(x) and three PTFE), exclusive of thesubstrate, with the sixth or outer layer being PTFE. The so-formed lighttransparent moisture barrier has a water vapor transmission rate of 250micrograms of water per in² of surface per 24 hours using the testmethod of Example 1.

Comparative Example B

This experiment is also similar to that of Example 1 with respect to theRF sputtering deposition in argon, the polyethylene naphthenatesubstrate and moisture transmission test method. In this experiment bothsides of the substrate film are coated with a layer of TiO₂ 150angstroms thick over which is deposited a layer of Teflon AF 500angstroms thick to produce a composite such as that illustrated inFIG. 1. The so-formed light transparent moisture barrier has a watervapor transmission rate of about 530 of micrograms of water per in²surface per 24 hours using the test method of Example 1.

Comparative Example C

This experiment is also similar to that of Example 1 with respect to theRF sputtering deposition in argon, the polyethylene naphthenatesubstrate and moisture transmission test method. In this experiment bothsides of the substrate film are coated with a layer of ZrO₂ 200angstroms thick over which is deposited a layer of Teflon AF 500angstroms thick to produce a four layer composite on the substrate suchas that illustrated in FIG. 1. The so-formed light transparent moisturebarrier has a water vapor transmission rate of about 300 micrograms ofwater per in² of surface per 24 hours using the test method of Example1.

Comparative Example D

This experiment is also similar to that of Example 1 with respect to theRF sputtering deposition in argon, the polyethylene naphthenatesubstrate and moisture transmission test method. In this experiment bothsides of the substrate film are coated with a layer of Al₂ O₃ 500angstroms thick over which is deposited a layer of (PTFE) 500 angstromsthick to produce a composite such as that illustrated in FIG. 1. Theso-formed light transparent moisture barrier has a water vaportransmission rate of about 300 micrograms of water per in² of surfaceper 24 hours using the test method of Example 1.

Comparative Example E

This experiment is similar to that of Example 1 with respect to the RFsputtering deposition in argon, the polyethylene naphthenate substrateand moisture transmission test method. In this experiment one side onlyof the substrate film is coated with a layer of SiO_(x) 500 angstromsthick over which is deposited a 500 angstrom thick layer of Teflon AF.This process is repeated twice to produce a composite (exclusive of thesubstrate) having six alternating layers of (three layers of SiO_(x) andthree layers of Teflon AF) with the sixth or outer layer being TeflonAF. The so-formed light transparent moisture barrier has a water vaportransmission rate of about 300 micrograms of water per in² of surfaceper 24 hours using the test method of Example 1.

Comparative Example F

This experiment is similar to that of Comparative Example D except thatTeflon AF is used instead of PTFE. The so-formed light transparentmoisture barrier has a water vapor transmission rate of about 300micrograms of water per in² of surface per 24 hours using the testmethod of Example 1.

It is understood that various other embodiments and modifications in thepractice of the invention will be apparent to, and can readily made by,those skilled in the art without departing from the scope and spirit ofthe invention disclosed above. Accordingly, it is not intended that thescope of the claims appended hereto be limited to the description setforth above, but rather that the claims be construed as encompassing allof the features of patentable novelty which reside in the presentinvention, including all features and embodiments which would be treatedas equivalents thereof by those skilled in the art to which theinvention pertains.

What is claimed is:
 1. A label/tester composite for an electrochemicalcell, said composite comprising a label and an electrochemical tester incontact with said label, said tester having a light transparent moisturebarrier for protecting said tester from moisture, wherein said moisturebarrier comprises a composite on a polymeric substrate, said moisturebarrier composite comprising at least one layer of amorphous siliconnitride and at least one layer of a hydrophobic fluorocarbon polymer,alternately deposited over each other, wherein the thickness of saidsilicon nitride and fluorocarbon polymer layers ranges between about 250to 2500 angstrom and between about 250 angstrom to about 1 micron,respectively, and wherein said moisture barrier is no greater than oneand one half mils thick.
 2. The label/tester composite of claim 1wherein said moisture barrier composite comprises at least two layers ofsaid silicon nitride and at least two layers of said fluorocarbonpolymer.
 3. The label/tester composite of claim 2 in which the layers ofsaid moisture barrier closest to said label are polymeric.
 4. Thelabel/tester composite of claim 1 in which the thickness of each of thefluorocarbon polymer layers is between about 300 and 5,000 angstroms. 5.The label/tester composite of claim 1 in which said moisture barrier haswater vapor permeability of less than 8 micrograms of water per squareinch of surface area over a twenty four hour period.
 6. The label/testercomposite of claim 5 wherein said fluorocarbon polymer comprises atleast one polymer selected from the group consisting of (i)polytetrafluoroethylene (PTFE), (ii) copolymers of tetrafluoroethylene(TFE) with hexafluoropropylene, (iii) copolymers of TFE withperfluoro(alkyl vinyl ethers), and (iv) polymers formed by reacting2,2-bistrifluoromethyl-4,5 difluoro 1,3dioxole (PDD) with at least onemonomer selected from the group consisting of PDD, TFE, vinylidenefluoride, chlorotrifluoroethylene, vinyl fluoride, perfluoro(alkyl vinylethers) and mixtures thereof.
 7. The label/tester composite of claim 6wherein said fluorocarbon polymer is formed by reacting said PDD with atleast one monomer selected from the group consisting of PDD, TFE,vinylidene fluoride, chlcrotrifluoroethylene, vinyl fluoride, perfluoro(alkyl vinyl ethers) and mixtures thereof.
 8. The label/tester compositeof claim 7 wherein said fluorocarbon polymer is a reaction product ofsaid PDD and said TFE.
 9. The label/tester composite of claim 5 whereinsaid moisture barrier composite comprises alternating layers of saidsilicon nitride and said fluorocarbon polymer.
 10. The label/testercomposite of claim 9 wherein said fluorocarbon polymer comprises atleast one polymer selected from the group consisting of (i) PTFE, (ii)copolymers of TFE with hexafluoropropylene, (iii) copolymers of TFE withperfluoro(alkyl vinyl ethers), and (iv) polymers formed by reacting2,2-bistrifluoromethyl-4,5-difluoro- 1,3-dioxole (PDD) with at least onemonomer selected from the group consisting of PDD, TFE, vinylidenefluoride, chlorotrifluoroethylene, vinyl fluoride, perfluoro(alkyl vinylethers) and mixtures thereof.